LONDON — Prince William and his wife, Catherine, Duchess of Cambridge, welcomed an 8-pound 6-ounce baby boy on Monday, sparking sprays of blue floodlights from Niagara Falls to New Zealand for a prince descended from kings and coal miners and now third in line to the British throne.

After two centuries of monarchy dominated by imposing women — Queen Victoria and the reigning Queen Elizabeth II — the birth of the little prince heralded the coming of an era of British kings. Should the new prince live a long and healthy life and barring unforeseen events, he will follow his grandfather, Prince Charles, and father, Prince William, to the halls of Buckingham Palace.

From inside the Lindo Wing of St. Mary's Hospital — where Diana, Princess of Wales, gave birth to him 31 years ago — Prince William, now a proud new father, issued a brief statement saying "we could not be happier."

The birth at 4:24 p.m. local time (11:24 a.m. Eastern time) — but kept secret for a good four hours — amounted to the ultimate showdown between British tradition and the 24-hour news cycle, as well as a rare nod to modernity by the world's highest-profile monarchy. Initially, an elegant official announcement delivered from the hospital by royal courier and posted behind the gates of Buckingham Palace was to be the first word to the world. But apparently concerned about being beaten by social media, and with press in a feeding frenzy since the duchess was admitted to the hospital about 6 a.m., the palace opted to scoop itself instead.

The official announcement was posted as billed. But a speedier electronic press release — along with a tweet — were used in a last-minute decision to disseminate the news more "quickly" and "simply," as the palace put it. Those are two words not often used to describe the British royal family.

The royal baby came as the handsome new parents and particularly the duchess — who, as the eldest daughter of run-of-the-mill Brits made good, was not born of nobility — have seemingly rebooted the Windsor brand. On Monday, evidence that international interest in the royal family has once again reached the apogee of the Diana years was literally spilling onto the sidewalks.

Outside the Lindo Wing, hundreds of journalists, many of whom had staked out the hospital for weeks, did live shots into the evening in a Babel of languages. They were jostling for position for the moment of truth, expected to come Tuesday, when the couple widely known as Will and Kate walk out of the hospital and offer a first glimpse of their still officially unnamed son.

Shortly after the birth, Prince Charles issued a statement reflecting on "grandparenthood," calling it "a unique moment in anyone's life" and saying he was "enormously proud and happy."

Prime Minister David Cameron called the arrival of the new prince "an important moment in the life of our nation."

In Washington, President Barack Obama said in a statement: "Given the special relationship between us, the American people are pleased to join with the people of the United Kingdom as they celebrate the birth of the young prince."

The prince is set to be a million-dollar baby — or a $383 million baby, to be more precise. That's the figure Britain's Center for Retail Research estimated would be the short-term economic windfall from the birth, ranging from sales of grandmotherly official teacups to a boom in champagne and beer.

Already, a photo of the duchess leaving a store with a white basket sent sales of similar items soaring. Ditto after a rumor that she had chosen a sky-blue stroller.

"The baby world has been waiting for this," said Olivia Robinson, creative director of Mamas & Papas, a British baby outfitter."Grandparents, mothers, are going to be watching. The high chair. The clothes. They are going to want them."

In a celebratory nation, the birth nevertheless left a flicker of disappointment for some longing to see a princess break one of the loftiest glass ceilings — the one towering above British royal heirs. Under a change that became law this year, a firstborn girl would not have been outranked by a younger brother.

But a boy was still more than enough reason to pop a cork. In the street party that broke out in front of Buckingham Palace, Paul Armstrong, 35, a London real estate agent, chugged down the pink sparkling wine he brought in hopes of a girl, while toasting baby blue.

"We were convinced it was a girl, partly because we have such a great queen now, but hey, we're happy it's a boy, and if he follows in the footsteps of his grandmother, he'll do great," he said.

For Americans of a certain stripe, a little thing like the Revolutionary War was not going to get between them and some ownership over this birth. Some who made a beeline for Buckingham Palace conceded their love affair with the royals was rooted in the largest absent figure on Monday — Diana, who, after her breakup with Prince Charles, died in a Paris car crash in 1997.

"I think Diana would love this and would be so excited to be a grandma," said Cheryl Hannah, a 62-year-old Ohio retiree.

William and his wife have been splitting their time between London and Anglesey, an island off the northwest coast of Wales, where the prince has worked as a search-and-rescue pilot for the Royal Air Force. But after the birth, many expect the pressure to grow for him to leave military service and begin taking up the full-time role of king-to-be (he is second in line after his father, Prince Charles).

The parents are poised to move later this year into Apartment 1A of Kensington Palace, formerly the home of the queen's sister, Princess Margaret. The residence has undergone a major facelift.

The British tabloids have reported that Catherine and the baby will spend the first six weeks after her release from the hospital with her parents, in Bucklebury, 55 miles west of London. A palace spokeswoman refused to confirm or deny that report.

If it happens, it may be the first of many breaks with tradition. Catherine's own non-royal upbringing — while privileged — is expected to prompt her to try for a more "normal" life for the young prince than palace culture has traditionally allowed. The daughter of former airline workers who struck it rich in business, Catherine is also the great-great-granddaughter of a coal miner.

Diana herself fiercely guarded the privacy of her sons but also wanted them to have typical childhood experiences, famously taking them on outings to McDonald's and Disneyland.

Some royal watchers expect William to be particularly protective, given his mother's death while being chased by paparazzi.

"This is going to be the hardest part for Prince William," said Dickie Arbiter, former spokesman to Queen Elizabeth II. "He still blames the press for the death of his mother, and he will be setting limits between the press and his child now. "

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Karla Adam in London and William Branigin in Washington contributed to this report.